I. Field of the Invention
The present invention relates generally to mobile radio communication systems. Specifically, the present invention relates to a mobile radio communication system that insures the acquisition of service from a service provider in cases where the mobile unit subscriber wishes to place an emergency call.
II. Description of the Prior Art
In wireless communication systems today, a mobile radio unit normally, when activated outside its home coverage area, attempts to acquire a servicing system based on a preferred roaming list (PRL) which is specified by the service carrier. Each service carrier provides specific PRLs based on roaming agreements with other carriers and the types of service a mobile radio unit customer is willing to purchase. Systems that are designated (or tagged) as xe2x80x9cnegativexe2x80x9d systems on the PRL will not be accessed by the mobile radio unit for routine communications. Mobile radio telephones are typically configured such that a user cannot make a phone call on a system which is considered a negative system as specified by the PRL.
In situations where a mobile radio unit is outside its home coverage area, there may be instances where a mobile user cannot acquire service using the systems included on the PRL. This might occur, for example, if the preferred service provider for a given geographic area was unable to provide service to the user. Alternatively, there could be instances where no preferred service provider was specified in the PRL for a given geographic area. In such cases, if the user needs to place an emergency call, e.g., a 911 call, the user might not be able to originate the call due to the absence of service from the home service provider and the lack of a preferred service provider on the PRL. It is an object of the present invention to provide the user with emergency service in cases such as those described above, so as to allow a mobile user to complete an emergency call in cases where service might otherwise be unavailable to the user, e.g., to complete the emergency call on a xe2x80x9cnegativexe2x80x9d system.
In accordance with a preferred embodiment, the present invention discloses a method and apparatus for acquiring emergency service from one or more candidate mobile radio communication systems. An attempt is made by the mobile radio unit to acquire normal non-emergency service. If the attempt to acquire normal non-emergency services fails and the user needs to originate an emergency call, the present invention scans an emergency scan list containing one or more candidate mobile radio communication systems and attempts to acquire emergency service from one of these systems. The emergency scan list is different from the normal preferred roaming list stored in the mobile radio unit. The invention originates an emergency call in accordance with the service acquired from the emergency scan list.